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LITTLE ROCK, Ark. -- The weekend shopping trip wasn't supposed to end like this. One minute, the grandmother of 3-year-old Acen King steered them toward the JC Penney in Little Rock, Arkansas. The next, the boy was fatally shot in the seat of her maroon Dodge Charger.

"My [grandson's] been shot," she wailed over the phone to a 911 dispatcher. "Oh my God!"

The shrill screams of the grandmother echoed through the sprawling mall parking lot Saturday night. The 911 calls released Monday capture the heartbreak of a woman who lost her grandson to gun violence after an apparent road rage incident.

Police continued to search Tuesday for the gunman who killed the child and have offered a $40,000 reward for information leading to an arrest and conviction.

The honks, then the havoc

The incident began Saturday evening when a motorist behind the grandmother grew agitated that she was not moving quickly enough at a stop sign, Little Rock Police Department spokesman Lt. Steven McClanahan said.

The man started honking his horn. The grandmother honked her horn. Then, police said, the man got out of his black Chevrolet Impala and fired into her car.

"One shot was fired and it went through the vehicle and hit the child," McClanahan said.

Not realizing that the boy had been hit, the woman drove to the JC Penney about 9 miles away. She realized her grandson was wounded when she went to get him out of the car, according to a police incident report.

"She didn't know he was shot," a bystander told the 911 operator after speaking with the grandmother.

A few minutes before 6:30 p.m., police received the first of several calls that the boy had been shot. The caller, describing what happened to the 911 operator, said the grandmother feverishly performed CPR after the child sustained a neck wound.

People gathered to watch as paramedics arrived and transferred the boy to Arkansas Children's Hospital, where he was pronounced dead. A 1-year-old child was also in the car at the time of the shooting, according to the police report.

'We're on your trail'

With the suspect still at large, Mercy Church Pastor Terrance Long called on people with information about the gunman to come forward.

"We want to let the killer know, we're on your trail," Long said.

Long pressured those who may know something about the shooting and the suspect but have failed to call police.

"The longer you hold out on information, the more you put yourself in the crossfire of it happening to you," Long said.

Under investigation

Police believe the grandmother and the slain boy had no relationship with the gunman.

"I certainly have no information to say that anyone in this family has done anything to cost this young person's life," Little Rock Police Department Chief Kenton Buckner told CNN affiliate KARK. "But this is about as frustrated as you can be as a public safety official or just a plain citizen."

The fatal shooting was Little Rock's 40th homicide of the year, police said. Last year, there were 31 homicides in the city.